Switching sub-system for distributed antenna systems using time division duplexing

ABSTRACT

A switching control module can optimize time division duplexing operations of a distributed antenna system (“DAS”). The switching control module can include a measurement receiver and a processor. The measurement receiver can measure signal powers of downlink signals in a downlink path of the DAS. The processor can determine start times for downlink sub-frames transmitted via the downlink path based on downlink signal powers measured by the measurement receiver exceeding a threshold signal power. The processor can identify a clock setting that controls a timing of switching signals used for switching the DAS between an uplink mode and a downlink mode. The processor can statistically determine a switching time adjustment for the clock setting based on switching time differentials between the clock setting and the start times. The processor can update the clock setting based on the switching time adjustment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 14/993,848filed Jan. 12, 2016 and titled “Switching Sub-System for DistributedAntenna Systems Using Time Division Duplexing,” which is a continuationof U.S. patent application Ser. No. 14/383,634, filed Sep. 8, 2014 andtitled “Switching Sub-System for Distributed Antenna Systems Using TimeDivision Duplexing,” which is a U.S. national phase application under 35U.S.C. 371 of International Patent Application No. PCT/IB2013/059803filed Oct. 30, 2013 and titled “Switching Sub-System for DistributedAntenna Systems Using Time Division Duplexing,” the entirety of each ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to telecommunication systemsand more particularly (although not necessarily exclusively) toswitching sub-systems for distributed antenna systems using timedivision duplexing.

BACKGROUND

Telecommunications operators use telecommunication systems to providesignal coverage to coverage zones in which wireless devices are located.A distributed system (“DAS”) may be used to extend the coverage of suchtelecommunication systems. Such distributed antenna systems includesignal paths between base stations or other signal sources operated bytelecommunication operators and remote antenna units positioned in oneor more geographical coverage areas.

In some implementations, a DAS may be configured for time divisionduplexing (“TDD”) operations in which downlink and uplink signals arerespectively transmitted and received using at least some commonfrequencies or common portions of a signal path. A DAS configured forTDD operations may include one or more switches for isolating downlinksignal paths from uplink signal paths.

In some cases, multiple telecommunication operators may use the same DASfor extending the coverage of their respective telecommunicationsystems. An entity responsible for configuring or otherwise operatingthe DAS may be independent of the telecommunication operators that usethe DAS. The entity being independent of the telecommunication operatorsmay present disadvantages. For example, it may be difficult orinfeasible to configure the switching operations of the DAS inaccordance with the TDD configuration used by the telecommunicationoperators.

Systems and methods for optimizing TDD switching operations for a DASare desirable.

SUMMARY

Certain aspects and features of the present disclosure are directed toswitching sub-systems for distributed antenna systems using timedivision duplexing.

In one aspect, a switching control module is provided for optimizingtime division duplexing (“TDD”) operations of a distributed antennasystem (“DAS”). The switching control module can include a measurementreceiver and a processor. The measurement receiver can measure signalpowers of downlink signals in a downlink path of the DAS. The processorcan determine start or end times for downlink sub-frames transmitted viathe downlink path based on downlink signal powers measured by themeasurement receiver exceeding a threshold signal power. The processorcan identify a clock setting that controls a timing of switching signalsused for switching the DAS between an uplink mode and a downlink mode.The processor can statistically determine a switching time adjustmentfor the clock setting based on switching time differentials between theclock setting and the start or end times. The processor can update theclock setting based on the switching time adjustment.

In another aspect, a TDD switching sub-system is provided that can bedisposed in a remote antenna unit of a DAS. The TDD switching sub-systemcan include one or more switches positioned in a downlink path from amaster unit to an antenna of the remote antenna unit or an uplink pathfrom the antenna to the master unit. The switches can selectivelyconnect the antenna of the remote antenna unit to the uplink path or thedownlink path. The TDD switching sub-system can also include ameasurement receiver communicatively coupled to the downlink path. Themeasurement receiver can measure downlink signal power in the downlinkpath. The TDD switching sub-system can also include a processor that iscommunicatively coupled to the measurement receiver and switches. Theprocessor can determine start or end times for downlink sub-framestransmitted via the downlink path based on downlink signal powersmeasured by the measurement receiver exceeding a threshold signal power.The processor can identify a clock setting that controls a timing ofswitching signals used for switching the DAS between an uplink mode anda downlink mode. The processor can statistically determine a switchingtime adjustment for the clock setting based on switching timedifferentials between the clock setting and the start or end times. Theprocessor can update the clock setting based on the switching timeadjustment.

In another aspect, a method is provided for optimizing switching timesfor a DAS that is configured for TDD operations. The method can involveidentifying a clock setting that controls the timing of switchingsignals provided to one or more switches positioned in an uplink path ora downlink path of the DAS. The switching signals can instruct theswitches to switch the DAS between an uplink mode and a downlink mode.The method can also involve determining start or end times for downlinksub-frames transmitted via the downlink path. Each start or end time canbe determined based on a measured signal power in the downlink pathexceeding a threshold signal power. The method can also involve updatingthe clock setting based on a switching time adjustment that isstatistically determined from multiple switching time differentials.Each switching time differential can include a respective differencebetween the clock setting and a respective one of the start or endtimes.

These illustrative aspects and features are mentioned not to limit ordefine the disclosure, but to provide examples to aid understanding ofthe concepts disclosed in this application. Other aspects, advantages,and features of the present disclosure will become apparent after reviewof the entire application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram depicting an example of a distributed antennasystem having a time-division duplex (“TDD”) switching sub-systemaccording to one aspect of the present disclosure.

FIG. 2 is a block diagram depicting an example of a remote antenna unitwith a TDD switching sub-system according to one aspect of the presentdisclosure.

FIG. 3 is a block diagram depicting an example of a switching controlmodule of the TDD switching sub-system of FIG. 2 according to one aspectof the present disclosure.

FIG. 4 is a flow chart depicting an example of a process for determiningan initial clock setting for the switching control module according toone aspect of the present disclosure.

FIG. 5 is a graph depicting examples of switching time differentialsbetween downlink sub-frames and switching signals provided according toan initial clock setting according to one aspect of the presentdisclosure.

FIG. 6 is a graph depicting an example of a statistical distribution ofswitching time differentials used to find a switching time adjustmentaccording to one aspect of the present disclosure.

FIG. 7 is a graph depicting examples of statistical distributions ofswitching time differentials affected by a signal-to-noise level in thedownlink path according to one aspect of the present disclosure.

FIG. 8 is a flow chart depicting an example of a process for determiningan optimized clock setting for the switching control module according toone aspect of the present disclosure.

FIG. 9 is a schematic depicting examples of a master unit and remoteantenna units for an optical TDD distributed antenna system that canutilize an optimized clock setting for a TDD switching sub-systemaccording to one aspect of the present disclosure.

DETAILED DESCRIPTION

Certain aspects and examples are directed to switching sub-systems for adistributed antenna system (“DAS”) configured for time divisionduplexing (“TDD”) operations. For example, the DAS can use a switchingsub-system to switch between an uplink mode for communicating TDDsignals in an uplink direction and a downlink mode for communicating TDDsignals in a downlink direction. The switching sub-system canautomatically determine switching times for the DAS based on determiningwhether a signal level for downlink signals exceeds a threshold level.One or more switches of the switching sub-system can switch a remoteantenna unit of the DAS to the downlink mode by selectively connectingone or more components of the downlink path in the remote antenna unitand disconnecting one or more components of a corresponding uplink pathin the remote antenna unit.

In accordance with some aspects, the switching sub-system can include aswitching control module that detects the downlink/uplink ratio of basestations in communication with the DAS. The switching control module candetermine an initial clock setting based on the downlink/uplink ratio.The initial clock setting can determine the timing for sending commandsignals to the switches of the switching sub-system that instruct theswitches to switch the DAS between an uplink mode and a downlink mode.

The switching control module can also optimize a clock setting thatcontrols switching times for the switches. Optimizing the switchingtimes can maximize or otherwise improve data throughput via the DAS. Theswitching control module can optimize the clock setting by determiningstart or end times for respective downlink sub-frames transmitted viathe downlink path. The switching control module can determine the startor end times based on when signal power measurements for the downlinkpath exceed a threshold signal power. The switching control module canstatistically determine a switching time adjustment based on a set ofswitching time differentials between the initial clock setting and thedetermined start or end times for the downlink sub-frames. For example,the switching time adjustment may be the statistical mean of the set ofswitching time differentials. The switching control module can updatethe clock setting based on the switching time adjustment.

The switching control module can be used to automatically determine aTDD configuration for one or more telecommunication operators using theDAS. Automatically determining the TDD configuration can reduce oreliminate the need for manual configuration of the DAS with respect toeach telecommunication operator. Reducing or eliminating the need formanual configuration of the DAS can reduce or avoid problems resultingfrom missing information with respect to the configuration settings ofdifferent telecommunication operators. The switching control module canalso compensate for uplink or downlink pulsing variation or otherdeficiencies components of the DAS in the uplink or downlink direction,such as a jitter or clock frequency drift experienced by one or morereference clock devices in the DAS.

Detailed descriptions of certain examples are discussed below. Theseillustrative examples are given to introduce the reader to the generalsubject matter discussed here and are not intended to limit the scope ofthe disclosed concepts. The following sections describe variousadditional aspects and examples with reference to the drawings in whichlike numerals indicate like elements, and directional descriptions areused to describe the illustrative examples but, like the illustrativeexamples, should not be used to limit the present disclosure.

FIG. 1 is a block diagram depicting an example of DAS 100 having a TDDswitching sub-system 110 according to one aspect. The DAS 100 caninclude a master unit 102 in communication with remote antenna units 104a, 104 b and with base stations 101 a, 101 b. In some aspects, differentbase stations can communicate signals associated with differenttelecommunication operators. The DAS 100 can be positioned in ageographical area (e.g., a stadium, an office building, etc.) to extendwireless communication coverage of the base stations 101 a, 101 b intogeographical coverage areas 108 a, 108 b.

The DAS 100 or other telecommunication system can include downlink pathsfor transporting downlink signals from the base stations 101 a, 101 b toone or more of the remote antenna units 104 a, 104 b. The DAS 100 canreceive downlink signals from the base stations 101 a, 101 b via a wiredor wireless communication medium. Downlink signals can include signalsprovided from the base stations 101 a, 101 b and transmitted by theremote antenna units 104 a, 104 b in the coverage areas 108 a, 108 b. Anon-limiting example of a remote antenna unit is a universal accesspoint.

The DAS 100 or other telecommunication system can also include uplinkpaths for transporting uplink signals from one or more of the remoteantenna units 104 a, 104 b to one of more of the base stations orrepeaters. Uplink signals are signals at frequencies in an uplinkfrequency band that are recovered or otherwise received by one or moreof the remote antenna units 104 a, 104 b from communication devices inthe coverage areas 108 a, 108 b.

The master unit 102 can communicate signals between the base stations101 a, 101 b and the remote antenna units 104 a, 104 b. An example of amaster unit 102 is a wireless conversion station. The master unit 102and remote antenna unit(s) 104 a, 104 b can communicate via any suitablecommunication medium. The communication medium can be any suitablemedium for providing a serial communication link between the master unit102 and the remote antenna unit 104 a, 104 b. In some aspects, thecommunication medium can be an optical fiber. In other aspects, thecommunication medium can include copper cables, microwave links, etc.The master unit 102 and remote antenna units 104 a, 104 b can includeanalog-to-digital and digital-to-analog converters for digitalcommunication over a serial link.

For illustrative purposes, FIG. 1 depicts a single master unit 102 incommunication with two base stations 101 a, 101 b and two remote antennaunits 104 a, 104 b. However, a distributed antenna system 100 caninclude any number of master units and any number of remote antennaunits for communicating signals between any number of base stations orother signal sources and any number of coverage areas.

A DAS 100 can include other devices in addition to master units, remoteantenna units, and extension units. For example, in some aspects, theDAS 100 may include a base station router or other interface device thatreceives signals from base stations 101 a, 101 b and provides thesignals to the master unit 102. In other aspects, the DAS 100 mayinclude one or more extension units that communicate signals between themaster unit 102 and the remote antenna units 104 a, 104 b.

The DAS 100 can be configured for TDD operations that support multipleoperators communicating signals via the DAS 100. For example, the DAS100 can switch between an uplink mode for communicating TDD signals inan uplink direction and a downlink mode for communicating TDD signals ina downlink direction.

The remote antenna units 104 a, 104 b can respectively include TDDswitching sub-systems 110 a, 110 b used to connect components of thedownlink path in response to detecting downlink signals having signallevels exceeding a threshold level. The TDD switching sub-systems 110 a,110 b can analyze downlink signals to determine if signal levels for thedownlink signals exceed specified threshold levels. Each of the TDDswitching sub-systems 110 a, 110 b can include switches that switch arespective one of the remote antenna units 104 a, 104 b to the downlinkmode by selectively connecting one or more components of the downlinkpath in the remote antenna unit and disconnecting one or more componentsof a corresponding uplink path in the remote antenna unit.

FIG. 2 is a block diagram depicting an example of a remote antenna unit104 with a TDD switching sub-system 110 according to one aspect. In adownlink direction, downlink signals received from the master unit 102via an interface 202 can traverse a downlink path 204 and can be coupledto an antenna 209 via an interface 208 for transmission to communicationdevices in a coverage area. In an uplink direction, uplink signalsreceived by the antenna 209 can be coupled to an uplink path 206 via theinterface 208 and can traverse the uplink path 206 for transmission tothe master unit 102 via the interface 202.

The TDD switching sub-system 110 can include one or more components ofthe downlink path 204 and the uplink path 206. For example, FIG. 2depicts a TDD switching sub-system 110 that includes a switching controlmodule 210, switches 212, 214 in the downlink path 204, and a switch 216in the uplink path 206. The switching control module 210 can be coupledto the downlink path 204 in any suitable manner. The switch 212 can bepositioned in the downlink path 204 between the interface 202 and apower amplifier 218. The switch 214 can be positioned in the downlinkpath 204 between the power amplifier 218 and the interface 208. Theswitch 216 can be positioned in the uplink path 206 between theinterface 208 and a low noise amplifier 220.

The switching control module 210 can control the operation of theswitches 212, 214, 216 to selectively allow communication of downlinksignals via the downlink path 204 or uplink signals via the uplink path206. The switching control module 210 can control the switches 212, 214,216 by sending switching signals to the switches 212, 214, 216 ordevices actuating the switches 212, 214, 216 (not depicted in FIG. 2).The switching control module 210 can be communicatively coupled to theswitches 212, 214, 216 or devices actuating the switches 212, 214, 216via any suitable mechanism. For example, the remote antenna unit 104 mayinclude a printed circuit board or other communication bus via whichswitching signals from the switching control module 210 can provided tothe switches 212, 214, 216 or devices actuating the switches 212, 214,216. For downlink transmission, the switching control module 210 canprovide switching signals that cause the switches 212, 214 to be closedand the switch 216 to be opened, thereby completing the downlink path204 between the interfaces 202, 208 and opening the uplink path 206between the interfaces 202, 208. For uplink transmission, the switchingcontrol module 210 can provide switching signals that cause the switches212, 214 to be opened and the switch 216 to be closed, thereby openingthe downlink path 204 between the interfaces 202, 208 and completing theuplink path 206 between the interfaces 202, 208. Any suitable switches212, 214, 216 can be used. Non-limiting example of suitable switches212, 214, 216 include RF switches, RF attenuators, digital attenuatorsin a digital signal path, digital switches interrupting a digital signalin a digital signal path, etc.

Although FIG. 2 depicts the switching control module 210 as a separatemodule coupled to the downlink path 204 for illustrative purposes, otherimplementations are possible. In some aspects, the downlink path 204 mayinclude one or more digital signal processing components, such as aprocessing device (e.g., an application-specific integrated circuit(“ASIC”), a field-programmable gate array (“FPGA”), etc.) The functionsof the switching control module 210 can be performed by the processingdevice using digital downlink signals in the downlink path 204 betweenthe interfaces 202, 208.

The switching control module 210 can provide switching signals based ona detection of downlink signals in the downlink path 204, an internalclock, or a combination thereof. For example, FIG. 3 is a block diagramdepicting an example of the switching control module 210 according toone aspect. The switching control module 210 can detect thedownlink/uplink ratio of the base stations 101 a, 101 b of other signalssources. The switching control module 210 can determine an initial clocksetting for the TDD switching sub-system based on the downlink/uplinkratio. The initial clock setting can determine the timing of sendingswitching signals to the switches 212, 214, 216. The switching controlmodule 210 can optimize switching times for the switches 212, 214, 216.Optimizing the switching times can maximize or otherwise improve datathroughput via the DAS 100.

The switching control module 210 can include a measurement receiver 302,a comparator 304, and a processor 306 communicatively coupled to amemory 308.

The measurement receiver 302 can include any suitable device formeasuring a signal power level in the downlink path 204. A non-limitingexample of a measurement receiver 302 is a power detector. Themeasurement receiver 302 can be coupled to the downlink path 204 in anysuitable manner, such as (but not limited to) a directional coupler.

The comparator 304 can include a first input coupled to an output of themeasurement receiver 302 and a second input coupled to a referencesource 312. The measurement receiver 302 can provide a voltage orcurrent representative of a signal power measurement for the downlinkpath 204 to the first input of the comparator 304. The reference source312 can provide a voltage or current representative of a thresholdsignal power to the second input of the comparator 304. The comparator304 can compare the representative voltages or currents for the downlinksignal power measurement and the threshold signal power. The comparator304 can output a voltage or current representative of whether thedownlink signal power measurement exceeds the threshold signal power.The threshold signal power can be modified by modifying the voltage orcurrent provided by the reference source 312.

The processor 306 can receive the voltage or current representative ofwhether the downlink signal power measurement exceeds the thresholdsignal power. The processor 306 can control switching operations of theTDD switching sub-system 100 based on the comparison of the downlinksignal power measurement and the threshold signal power by executing aswitching control engine 310 or other executable instructions stored tothe memory 308, as described in further detail below. The processor 306can control the switching operations by generating switching signalsthat are provided to the switches 212, 214, 216 or the devices used foractuating the switches 212, 214, 216.

The processor 306 can include any device or group of devices suitablefor accessing and executing executable instructions stored in the memory308. Non-limiting examples of the processor 306 include amicroprocessor, an ASIC, a FPGA, or other suitable processing device.The processor 306 may include one processor or any number of processors.The memory 308 may be any non-transitory computer-readable mediumcapable of tangibly embodying executable instructions and can includeelectronic, magnetic, or optical devices. Examples of memory 308 includerandom access memory (“RAM”), read-only memory (“ROM”), magnetic disk,an ASIC, a configured processor, or other storage device. Instructionscan be stored in memory 308 as executable code. The instructions caninclude processor-specific instructions generated by a compiler and/oran interpreter from code written in any suitable computer-programminglanguage, such as C, C++, C#, Visual Basic, Java, Python, Perl,JavaScript, and ActionScript.

Although FIG. 3 depicts a switching control module 210 including acomparator 304 for outputting a signal indicative of whether thedownlink signal power exceeds a threshold signal power, otherimplementations are possible. For example, in some aspects, thecomparator 304 and the reference source 312 can be omitted. Theprocessor 306 can communicate with the measurement receiver 302 toobtain data describing signal power levels in the downlink path 204. Inone non-limiting example the measurement receiver 302 can have an analogoutput electrically connected to the processor 306. The measurementreceiver 302 can provide a voltage or a current to the processor 306 viathe analog output. The voltage or current can be equivalent to orotherwise indicative of the measured power level in the downlink path204. In another non-limiting example, the measurement receiver 302 canprovide a digital output signal to the processor 306 that represents themeasured power level in the downlink path 204. In additional oralternative aspects, the measurement receiver 302 can include a digitalinput that is coupled to the downlink path 304.

The processor 306 can compare the data obtained from the measurementreceiver 302 with data stored in the memory 308 that describes thethreshold signal power. The threshold signal power can be modified byproviding updated data describing the threshold signal power to theprocessor 306 for storage in the memory 308.

FIG. 4 is a flow chart depicting an example of a process 400 fordetermining an initial clock setting for the switching control module210 according to one aspect. For illustrative purposes, the process 400is described with respect to the implementation of the TDD switchingsub-system 110 and the switching control module 210 described above withrespect to FIGS. 2-3. Other implementations, however, are possible.

The process 400 can be used to automatically determine a TDDconfiguration for one or more telecommunication operators using the DAS100. Automatically determining the TDD configuration can reduce oreliminate the need for manual configuration of the DAS 100 with respectto each telecommunication operator. Reducing or eliminating the need formanual configuration of the DAS 100 can reduce or avoid problemsresulting from missing information with respect to the configurationsettings of different telecommunication operators.

The process 400 involves obtaining multiple downlink frame samples bymeasuring signal power in a downlink path of a TDD DAS at multipletimes, as depicted in block 410. For example, the processor 306 canexecute the switching control engine 310 to sample data from themeasurement receiver 302 or the comparator 304 at intervals specified bythe switching control engine 310. For each interval, the processor 306can store data in the memory 308 describing whether the signal power inthe downlink path 204 exceeds the threshold power. The signal power inthe downlink path 204 exceeding the threshold power can indicate that adownlink frame is being transmitted via the downlink path 204. Thesignal power in the downlink path 204 being less than or equal to thethreshold power can indicate that a downlink frame is not beingtransmitted via the downlink path 204 and that an uplink frame is beingtransmitted via the uplink path 206. In some aspects, the measurementreceiver 302 can measure the signal power in the downlink path 204 atintervals specified by the processor 306. In other aspects, themeasurement receiver 302 can continuously measure the signal power inthe downlink path 204. The processor 306 can sample power measurementsfrom measurement receiver 302 or sample current or voltage levels at theoutput of the comparator 304 at the specified intervals.

The process 400 further involves determining a downlink/uplink ratio forthe TDD DAS based on the downlink frame samples, as depicted in block420. For example, the switching control engine 310 can access datadescribing different downlink/uplink ratios for different TDDconfigurations. Different TDD configurations may communicate TDD signalsin a specified ratio between the uplink and downlink sub-frames. A framecan be a period of time a TDD system switches between sending uplink anddownlink data in according to a specified sequence. A frame can includeuplink sub-frames during which uplink data is transmitted and downlinksub-frames during which uplink data is transmitted. The downlink/uplinkratio can include the number of individual downlink and uplinksub-frames and the duration of each sub-frame.

The process 400 further involves determining an initial clock settingfor the switching control module 210 based on the downlink/uplink ratio,as depicted in block 430. For example, the processor 306 can execute theswitching control engine 310 to determine the initial clock setting. Theclock setting can be used to determine when the processor 306 provides aswitching signal to the switches 212, 214, 216. For example, theprocessor 306 can provide the switching signal every t_(clk) seconds,milliseconds, microseconds, or other suitable unit of time. The value oft_(clk) used for the clock setting can correspond to the TDDconfiguration of a telecommunication operator using the DAS 100. Aninitial value of t_(clk) can be selected based on a TDD configurationdetermined from the downlink/uplink ratio.

A TDD configuration of a base station using the DAS 100 can bedetermined by identifying downlink sub-frames and uplink sub-framesduring a TDD frame can be used to determine. A downlink/uplink ratio cancorrespond to a given TDD configuration. For example, an LTE systemconfigured for TDD operation can include a first configuration with aratio of two downlink sub-frames to three uplink sub-frames, a secondconfiguration with a ratio of three downlink sub-frames to two uplinksub-frames, a third configuration with a ratio of four downlinksub-frames to one uplink sub-frames, etc. In some aspects, the switchingcontrol engine 310 can select a TDD configuration based on astandardized downlink/uplink ratio in a telecommunication standard, suchas a 3rd Generation Partnership Project (“3GPP”) specification.Selecting the TDD configuration based on a standardized downlink/uplinkratio in a telecommunication standard can minimize or otherwise reduceerrors with respect to incorrect switching intervals. In other aspects,the switching control engine 310 can be configured via user input withone or more specified TDD configurations corresponding to one or morespecified downlink/uplink ratios.

The switching control engine 310 can compare the downlink/uplink ratiodetermined using the measurement receiver 302 to data stored to thememory device that describes various TDD configurations. The switchingcontrol engine 310 can identify the TDD configuration for an operatorusing the DAS 100 based on the comparison of the determineddownlink/uplink ratio with the stored data describing various TDDconfigurations. The switching control engine 310 can select an initialvalue for t_(clk) that causes the processor 306 to send switchingsignals to the switches 212, 214, 216 in accordance with the identifiedTDD configuration.

In some aspects, the DAS 100 can be set to an offline mode forperforming the process 400. For example, the DAS 100 may beautomatically set to an initialization mode upon entering operation. Aninitialization or other offline mode can be used to set one or moresystem parameters of the DAS 100 used for TDD operation. In an offlinemode, the switching control module 210 may perform one or moreconfiguration operations based on signal power measurements in thedownlink path 204 without controlling the switches 212, 214, 216. Forexample, in an offline mode, the switches 212, 214, 216 may be set to anopen position such the DAS 100 does not communicate signals between thebase stations 101 a, 101 b and the coverage areas 108 a, 108 b.

The initial clock setting t_(clk) may roughly approximate the TDDconfiguration for an operator using the DAS 100. However, slightdiscrepancies may exist between the times at which downlink sub-framesbegin and the times at which the switching control module 210 providesswitching signals to the switches 212, 214, 216. For example, FIG. 5 isa graph depicting examples of switching time differentials betweendownlink sub-frames 502 a-n and switching signals 504 a-n providedaccording to an initial clock setting according to one aspect. Each ofthe switching time differentials is a delay between the start of arespective one of the downlink sub-frames 502 a-n and a time at which arespective one of the switching signals 504 a-n is provided to theswitches 212, 214, 216.

The switching control module 210 can optimize or otherwise improve theclock setting t_(clk) based on a switching time adjustment Δt_(adj)statistically determined from a set of switching time differentialsΔt_(n). For example, for one or more of the downlink sub-frames 502 a-n,the processor 306 can compare each of the clock settingst_(clk,1 . . . n) with a respective one of the times t_(DL,1 . . . n) atwhich a downlink signal power greater than a threshold signal power isdetected by the switching control module 210.

The processor can determine each switching time differentialΔt_(n)=|t_(clk,n)−t_(DL,n)−t_(offset)|. The offset value t_(offset) canbe a configurable static offset between the switching point determinedby the measurement receiver 302 and the point in time when the switchingpoint is required to be set. The switching control module 210 can beconfigured to detect a threshold signal power that is substantiallyhigher than the noise in the downlink path 204, thereby maintaining ahigh signal-to-noise ratio and a low statistical variance. The offsetvalue t_(offset) can be used if it is desirable to switch between theuplink and downlink mode prior to the signal power in the downlink path204 exceeding the high threshold signal power. The offset valuet_(offset) can be selected based on the threshold signal power used bythe switching control module 210, the telecommunication standard usedfor downlink signals in the downlink signal path 204, the use of the DAS100 by multiple operators, or the transmission of multi-channel signalsvia the DAS 100. In some aspects, the switching time differential Δt_(n)can be determined without using an offset value t_(offset).

The statistical variation of a determined switching point over time canbe caused by one or more processes in combination with one another. Onenon-limiting example of a source of the variation is the signal-to-noiselevel of the signal measured by the measurement receiver 302. Anothernon-limiting example of a source of variation is the jitter and drift ofa reference clock used by the switching engine 310 or other clocks inDAS 100 or the base stations 101 a, 101 b. Another non-limiting exampleof a source of variation is noise in the associated with the referencesource 312. Another non-limiting example of a source of variation isthat high power uplink signals can be coupled to the downlink path 204due to missing isolation between the uplink and downlink paths at themaster unit 102. The various source of variation can combine with oneanother to cause a statistical variation in the switching point.

FIG. 6 is a graph depicting an example of a statistical distribution ofswitching time differentials Δt_(n) used to find a switching timeadjustment Δt_(adj). Sampled values for Δt_(n) can be obtained overdifferent frames in which an operator using the DAS 100 switches betweenan uplink mode and a downlink mode. The switching control engine 310 cangenerate or otherwise obtain a statistical distribution of the sampledvalues for Δt_(n). The switching control engine 310 can determine theswitching time adjustment Δt_(adj) based on the statisticaldistribution. A non-limiting example of a switching time adjustmentΔt_(adj) statistically determined from sampled values for Δt_(n) is amean value Δt_(mean) of the sampled values for Δt_(n), as depicted inFIG. 6.

The signal-to-noise level in the downlink path 204 can impact thestatistical distribution of the sampled values of Δt_(n). For example,FIG. 7 is a graph depicting examples of statistical distributions ofswitching time differentials Δt_(n) affected by a signal-to-noise levelin the downlink path 204. A statistical distribution 602 of switchingtime differentials Δt_(n) represented by the solid line may obtainedfrom a downlink path 204 having a lower signal-to-noise ratio than thestatistical distribution 604 represented by the dashed line. The lowersignal-to-noise ratio can cause the statistical distribution 602 ofswitching time differentials Δt_(n) to have a wider range of values thanthe statistical distribution 604.

FIGS. 6-7 depict symmetrical or nearly symmetrical statisticaldistributions of the sampled values of Δt_(n). However, in some aspects,the statistical distribution of the sampled values of Δt_(n) may beasymmetrical. For example, the statistical distribution may be wider forearlier times and narrow for later times due to the higher signal level.

The switching control module 210 can use a switching time adjustmentΔt_(adj) to optimize or otherwise improve the clock setting used by theswitching control module 210. FIG. 8 is a flow chart depicting anexample of a process for determining an optimized clock setting for theswitching control module according to one aspect.

The process 700 involves identifying a clock setting that controlstiming for providing switching signals to one or more switches thatinstruct the switches to switch the distributed antenna system betweenan uplink mode and a downlink mode, as depicted in block 710. Forexample, the switching control engine 310 executed by the processor 306can determine a clock setting for providing switching signals to one ormore of the switches 212, 214, 216.

In some aspects, identifying the clock setting can include identifyingan initial clock setting for the switching control module 210, such as(but not limited to) a clock setting determined using a process 400. Forexample, the clock setting can be determined or otherwise identifiedduring an offline mode for the DAS 100 in which no switching signals areprovided to the switches 212, 214, 216.

In other aspects, the identified clock setting can be a current clocksetting for a DAS 100 in an online mode in which signals arecommunicated with coverage areas 108 a, 108 b. The current clock settingcan be the clock setting used for providing switching signals to theswitches 212, 214, 216 in the online mode of the DAS 100. The switchingcontrol engine 310 can identify the current clock setting and performadditional operations to optimize or otherwise update the current clocksetting.

The process 700 further involves determining start or end times forrespective downlink sub-frames transmitted via a downlink path of thedistributed antenna system, as depicted in block 720. For example, theswitching control engine 310 can receive or otherwise access datadescribing power measurements by the measurement receiver 302. Theswitching control engine 310 can identify a start time for a respectivedownlink sub-frame based on a power measurement indicating that a signalpower in the downlink path 204 exceeds the threshold signal power. Theswitching control engine 310 can identify an end time for a respectivedownlink sub-frame based on a power measurement indicating that a signalpower in the downlink path 204 drops from a level exceeding thethreshold signal power to a level below the threshold signal power.

The process 700 further involves statistically determining a switchingtime adjustment based on switching time differentials between the clocksetting and the respective start times, as depicted in block 730. Forexample, the switching control engine 310 can determine a switching timeadjustment that is a mean or other statistical attribute of a set ofsample switching time differentials, as described above with respect toFIGS. 5-6.

The process 700 further involves updating the clock setting based on theswitching time adjustment, as depicted in block 740. For example, theswitching control engine 310 can update the current clock settingt_(clk,current) to an updated clock setting t_(clk,updated) based on thefunction t_(clk,updated)=t_(clk,current)+Δt_(adj). In some aspects, theswitching control engine 310 can detect an end of a current TDD frame orsub-frame based on power measurements from the measurement receiver 302.The switching control engine 310 can generate switching signals for theswitches 212, 214, 216 at intervals of t_(clk,updated) after detectingthe end of the current TDD frame or sub-frame.

The TDD switching sub-system can be implemented in any suitable DAS 100configured for TDD operations. For example, FIG. 9 is a schematicdepicting examples of a master unit 102 and remote antenna units 104 a-nfor an optical TDD distributed antenna system that can utilize anoptimized clock setting for a TDD switching sub-system according to oneaspect.

The master unit 102 can include splitter-combiners 802 a-n for isolatinguplink and downlink signals communicated with base stations or othersignal sources. The master unit 102 can also include mixers 803 a-n andlocal oscillators 804 a-n for frequency-shifting downlink signals tointermediate frequency (“IF”) bands, as described in greater detailbelow. The master unit 102 can also include a combiner 806 for combiningdownlink signals from different operators for serial transmission toremote antenna units 104 a-n. The master unit 102 can also include anelectrical-to-optical converter 808 for converting the serializedelectrical downlink signals into serialized optical downlink signals.The serialized optical downlink signals can be transmitted to the remoteantenna units 104 a-n via the optical communication link 811. The masterunit 102 can also include an optical-to-electrical converter 812 forconverting optical uplink signals received via the optical communicationlink 811 into serialized electrical uplink signals. The master unit 102can also include a splitter 814 for separating the serialized electricaluplink signals into separate uplink signals for transmission to basestations or other receivers of uplink signals.

The remote antenna units 104 a-n can include respective opticalsplitter-combiners 816 a-n for isolating optical downlink signals fromoptical uplink signals. The remote antenna units 104 a-n can alsoinclude respective optical-to-electrical converters 818 a-n forconverting optical downlink signals into electrical downlink signals.The remote antenna units 104 a-n can also include respective mixers 820a-n and local oscillators 821 a-n for frequency shifting downlinksignals to RF frequency bands, as described in detail below. The remoteantenna units 104 a-n can also include respective bandpass filters 822a-n for attenuating unwanted frequency components of the RF downlinksignals outputted by the mixers 820 a-n. The remote antenna units 104a-n can also include switching control modules 210 a-n and switches 212a-n, 214 a-n, 216 a-n that perform the same or similar functions withrespect to the power amplifiers 218 a-n and low noise amplifiers 220 a-nas described above with respect to FIG. 2. The remote antenna units 104a-n can also include respective circulators 824 a-n for couplingdownlink signals from the downlink paths to the antennas 209 a-n and forcoupling uplink signals from the antennas 209 a-n to the uplink paths.The remote antenna units 104 a-n can also include respectiveelectrical-to-optical converters 828 a-for converting electrical uplinksignals to optical uplink signals for transmission via the opticalcommunication link 811.

Multiple telecommunication operators utilizing the DAS 100 can use acommon optical communication link 811 between the master unit 102 andthe remote antenna units 104 a-n. In some aspects, the DAS 100 cansupport an “uncoordinated operator mode.” In the uncoordinated operatormode, different operators using the DAS 100 do not coordinate with oneanother in switching between an uplink TDD mode and a downlink TDD mode.

The DAS 100 can be configured to reduce or eliminate uplink blocking byunsynchronized operators transmitting signals using adjacentfrequencies. For example, downlink signals from multiple operators canbe closely spaced within a frequency band (e.g., a few MHz). The mixers803 a-n and the local oscillators 804 a-n of the master unit 102 can beused to frequency-shift downlink signals to IF bands. Frequency shiftingthe downlink signals to IF bands can separate downlink signals fromuncoordinated operators use closely spaced frequencies for transmittingTDD signals. The mixers 820 a-n and local oscillators 821 a-n of theremote antenna units 104 a-n can be used to frequency-shift the IFdownlink signals back to RF bands for transmission. A reference clock805 in the master unit 102 can be used for synchronizing the localoscillators 804 a-n, 821 a-n. In some aspects, the reference clock 805can also be used for synchronizing the reference source 312 used by theswitching control module 210. The reference clock 805 can becommunicatively coupled to the local oscillators 804 a-n via anysuitable mechanism, such as a printed circuit board or othercommunication bus (not depicted in FIG. 9). Signals from the referenceclock 805 can be communicated from the master unit 102 to the remoteantenna units 104 a-n via the optical communication link 811.

The foregoing description of aspects and features of the disclosure,including illustrated examples, has been presented only for the purposeof illustration and description and is not intended to be exhaustive orto limit the disclosure to the precise forms disclosed. Numerousmodifications, adaptations, and uses thereof will be apparent to thoseskilled in the art without departing from the scope of this disclosure.Aspects and features from each example disclosed can be combined withany other example. The illustrative examples described above are givento introduce the reader to the general subject matter discussed here andare not intended to limit the scope of the disclosed concepts.

What is claimed is:
 1. A switching control module for a time divisionduplexing (TDD) communications system comprising a master unit and atleast one remote antenna unit that is communicatively coupled to themaster unit by an uplink path and a downlink path, the modulecomprising: a processor coupled to a memory; wherein the processor isconfigured to send control signals to at least one switch based onswitching times controlled by a clock setting, wherein the clock settingis determined by the processor as a function of an initial clock settingbased on a downlink:uplink sub-frame ratio that is adjusted by astatistically based clock setting adjustment and a downlink path signalpower measurement; and wherein the at least one switch is positioned inthe TDD communications system and the control signals instruct the atleast one switch to switch the TDD communications system between anuplink mode and a downlink mode.
 2. The module of claim 1, wherein thedownlink:uplink sub-frame ratio is determined by sampling a signal powerof multiple downlink fames in the downlink path.
 3. The module of claim1, wherein the downlink:uplink sub-frame ratio comprises a ratio of: a)uplink sub-frames communicated by the master unit to at least one basestation, to b) downlink sub-frames received by the master unit from theat least one base station.
 4. The module of claim 1, wherein thedownlink:uplink sub-frame ratio comprises a ratio of: a) uplinksub-frames communicated by the master unit to a plurality of basestations, to b) downlink sub-frames received by the master unit from theplurality of base stations.
 5. The module of claim 1, furthercomprising: a measurement receiver configured for measuring a signalpower in the downlink path; and a comparator device having an inputcoupled to the measurement receiver and an output coupled to theprocessor, wherein the comparator device is configured for comparing athreshold signal power with a power measurement received from themeasurement receiver via the input and providing a signal to theprocessor via the output that is indicative of whether the powermeasurement exceeds the threshold signal power.
 6. The module of claim1, wherein the memory comprises a plurality of TDD configurations;wherein the processor selects the initial clock setting by selecting afirst clock setting associated with a first TDD configuration from theplurality of TDD configuration based on the downlink:uplink sub-frameratio; and wherein the processor calculates the clock setting adjustmentstatistically from a set of switching time differentials, wherein eachswitching time differential of the set of switching time differentialsis a difference between a start of a respective downlink subframe asdetermined from the downlink path signal power measurement and a time atwhich a respective one of the control signals is provided to the atleast one switch.
 7. The module of claim 6, wherein the processor isconfigured determine the switching time adjustment by: determining starttimes or end times for respective downlink sub-frames transmitted viathe downlink path, wherein the processor determines each start time orend time based on the signal power measured by a measurement receiverexceeding a threshold signal power; and statistically determining theswitching time adjustment from multiple switching time differentials,wherein each of the switching time differentials comprises a respectivedifference between the initial clock setting and a respective start timeor end time.
 8. A method for controlling a time division duplexing (TDD)communications system comprising a master unit and at least one remoteantenna unit that is communicatively coupled to the master unit by anuplink path and a downlink path, the method comprising: determining aclock setting as a function of an initial clock setting based on adownlink:uplink sub-frame ratio that is adjusted by a statisticallybased clock setting adjustment and a downlink path signal powermeasurement; and sending control signals to at least one switch based onswitching times controlled by the clock setting; wherein the at leastone switch is positioned in the TDD communications system and thecontrol signals instruct the at least one switch to switch thecommunications system between an uplink mode and a downlink mode.
 9. Themethod of claim 8, wherein the downlink:uplink sub-frame ratio isdetermined by sampling a signal power of multiple downlink fames in thedownlink path.
 10. The method of claim 8, wherein the downlink:uplinksub-frame ratio comprises a ratio of: a) uplink sub-frames communicatedby the master unit to at least one base station, to b) downlinksub-frames received by the master unit from the at least one basestation.
 11. The method of claim 8, wherein the downlink:uplinksub-frame ratio comprises a ratio of: a) uplink sub-frames communicatedby the master unit to a plurality of base stations, to b) downlinksub-frames received by the master unit from the plurality of basestations.
 12. The method of claim 8, further comprising: measuring asignal power in the downlink path with a measurement receiver; andcomparing a threshold signal power with a power measurement receivedfrom the measurement receiver and providing a signal to a processor thatis indicative of whether the power measurement exceeds the thresholdsignal power.
 13. The method of claim 8, further comprising: selectingthe initial clock setting by selecting a first clock setting associatedwith a first TDD configuration from a plurality of TDD configurationstored in a memory based on the downlink:uplink sub-frame ratio; andcalculating the clock setting adjustment statistically from a set ofswitching time differentials, wherein each switching time differentialof the set of switching time differentials is a difference between astart of a respective downlink sub-frame as determined from the downlinkpath signal power measurement and a time at which a respective one ofthe control signals is provided to the at least one switch.
 14. Themethod of claim 13, calculating the clock setting adjustment comprises:determining start times or end times for respective downlink sub-framestransmitted via the downlink path, wherein the processor determines eachstart time or end time based on the signal power measured by ameasurement receiver exceeding a threshold signal power; andstatistically determining the switching time adjustment from multipleswitching time differentials, wherein each of the switching timedifferentials comprises a respective difference between the initialclock setting and a respective start time or end time.
 15. A timedivision duplexing (TDD) communications system, the system comprising: amaster unit; at least one remote antenna unit that is communicativelycoupled to the master unit by an uplink path and a downlink path; atleast one switch positioned in the TDD communications system and thecontrol signals instruct the at least one switch to switch thecommunications system between an uplink mode and a downlink mode; and aswitching control module comprising a processor coupled to a memory;wherein the processor is configured to send control signals to at leastone switch based on switching times controlled by a clock setting,wherein the clock setting is determined by the processor as a functionof an initial clock setting based on a downlink:uplink sub-frame ratiothat is adjusted by a statistically based clock setting adjustment and adownlink path signal power measurement.
 16. The system of claim 15,wherein the memory comprises a plurality of TDD configurations; whereinthe processor selects a # the initial clock setting by selecting a firstclock setting associated with a first TDD configuration from theplurality of TDD configuration based on the downlink:uplink sub-frameratio; and wherein the processor calculates a the clock settingadjustment statistically from a set of switching time differentials,wherein each switching time differential of the set of switching timedifferentials is a difference between a start of a respective downlinksub-frame as determined from the downlink path signal power measurementand a time at which a respective one of the control signals is providedto the at least one switch.
 17. The system of claim 15, wherein thedownlink:uplink sub-frame ratio is determined by sampling a signal powerof multiple downlink frames in the downlink path.
 18. The system ofclaim 15, wherein the switching control module is located in the atleast one remote antenna unit.
 19. The system of claim 15, wherein thedownlink:uplink sub-frame ratio comprises a ratio of: a) uplinksub-frames communicated by the master unit to at least one base station,to b) downlink sub-frames received by the master unit from the at leastone base station.
 20. The system of claim 15, wherein thedownlink:uplink sub-frame ratio comprises a ratio of: a) uplinksub-frames communicated by the master unit to a plurality of basestations, to b) downlink sub-frames received by the master unit from theplurality of base stations.